Airplane thrust reversers come in a variety of designs depending on the engine manufacturer, the engine configuration, and the propulsion technology being utilized. Thrust reversers for turbofan engines 10 such as the one shown in FIG. 1 are typically reversed in three ways. Cascade-type thrust reversers are located at an engine's midsection and redirect fan flow air 18 through cascade vanes 16 positioned on the engine periphery. Cascade-type reversers are normally used on high-bypass ratio engines. Target-type thrust reversers, sometimes called clamshell reversers, utilize two doors to block the entire jet efflux. These doors are in the aft portion of the engine and form the rear part of the nacelle. Target reversers are typically used with low-bypass ratio engines. Pivot door thrust reversers are similar to cascade-type thrust reversers except that no cascade vanes are provided. Instead, four doors on the engine nacelle blossom outward to redirect flow.
A cascade-type thrust reverser works as follows. Referring to FIG. 2, an engine fan case 12 includes a pair of semi-circular thrust reverser translating sleeves 14 (sometimes called cowls) that are positioned circumferentially on the outside of the fan case 12 and that cover a plurality of cascade vanes 16 (i.e., non-rearwardly facing air vents.) The cascade vanes 16 are positioned between the thrust reverser sleeves 14 and the bypass air flow path 18. Referring to FIGS. 2 and 3, a series of blocker doors 20 are mechanically linked to the thrust reverser sleeves 14 via a drag link 22 rotatably connected to an inner wall 24 that surrounds the engine case 26. In their stowed position, the blocker doors 20 form a portion of the inner wall and are therefore oriented parallel to fan air 18 flow. When the thrust reversers are activated, the thrust reverser sleeves 14 translate aft, causing the blocker doors 20 to rotate into a deployed position in which they block the fan air flow passage. This also causes the cascade vanes 16 to be exposed and the fan air 18 to be redirected out the cascade vanes. The re-direction of fan air 18 in a forward direction works to slow the airplane.
Still referring to FIG. 3, the thrust reverser sleeves 14 are operated by one or more hydraulic actuators 28 per engine. The actuators 28 are attached between a stationary torque box 30 and the translating sleeve. The actuators 28 interconnect with each other via a synchronization mechanism, such as a flexible shaft 32. The synchronization mechanism ensures that the actuators move at the same rate. The torque box 30 also provides structural support for the synchronization mechanism and the cascade vanes 16. As shown in FIG. 2, the torque box is typically formed as a pair of rigid semicircular beams located at the forward end of the fan case 12 (i.e., just forward of the cascade vanes.).
An actuation activation system translates the thrust reverser sleeves 14 from a locked and stowed position to an unlocked and translated position for reverse thrust. Due to significant physical forces present during flight that can work to push the translating sleeve 14 to an open position, current actuation systems include a number of ways of preventing uncommanded translation. For example, it is known to provide actuators that are capable of locking in order to retain the thrust reverser sleeve in the stow position. Or, an electrically-operated synchronization shaft lock 34 may be provided to control synchronization shaft movement. It is also known to provide automatic restow capability in which dedicated system control logic automatically causes the actuators 28 to stow the thrust reverser during detection of rearward movement of the sleeves 14.
One known auto-restow arrangement is described below with reference to FIG. 4. In this arrangement, two electric proximity sensors 36, 38 are mounted to the aft side of the torque box 30 and are facing rearward. Two spring-loaded targets 40, 42 are affixed to the translating sleeve 14. The sensors 36, 38 are targeted to a "normally near" condition (i.e., they are adjusted to expect under normal conditions the return signal from their target to be from a particular pre-defined "near" distance.) One of these sensors 36 is used for locating the position of the translating sleeve. The other sensor 38 is used for sleeve control by indicating an unlocked thrust reverser condition to the actuation activation system.
When the translating sleeve 14 is stowed for normal engine forward thrust, the targets 40, 42 are sensed by the sensors 36, 38 and the auto restow control logic is not accessed. If the sleeve moves aft, either powered or unpowered, the targets 40, 42 move away from the sensors 36, 38. This causes the distance between the sensors and the targets to increase and the sensors to trigger. Upon triggering, the sensors 36, 38 send a signal to the actuation activation system which energizes the auto restow control logic which immediately attempts to restow the thrust reversers. The auto-restow system is activated only when both targets are triggered by translation of the sleeve. This is referred to as `AND` logic 44 and is shown in FIG. 8A.
During normal operations, the sleeve 14 moves relative to the torque box 30 because of aerodynamic loads, vibrations, and relative motion between the engine and nacelle structures. Relative motion, however, can result in the targets being sensed in the "far" condition, which in turn trips one or both sensors 36, 38 and energizes the auto restow function, even though the sleeve is in fact still in its stowed and locked position.
Another undesirable aspect of this arrangement is that it is difficult and time consuming to position the sensors and target. To ensure proper detection of the target by the sensor, a specific required distance must be present between the sensors 36, 38 and the targets 40, 42. Prior to use, a mechanic must adjust the distance until it is within an acceptable range of values. This is done by using an iterative process, since the proximity sensor and target are covered by the translating sleeve 14. In particular, a mechanic must repeatedly test and readjust the location of the target until the required distance is obtained. Typically, the mechanic applies clay or other deformable substance to either the target (or the sensor.) The mechanic then closes and reopens the sleeve. The mechanic measures the resulting thickness of clay. Using this information, the mechanic calculates an adjustment to the position of the target. After the adjustment is made and more clay is added, the sleeve is once again closed and reopened. The mechanic again checks the clay thickness to see if the proper distance has been attained. If not, the process is repeated until it is within acceptable limits. As can be appreciated, this is a very labor intensive and cumbersome process.
Thus, a need exists for an improved actuation activation system in which the thrust reverser is automatically restowed. The ideal system would be easy to install and easy to calibrate without requiring labor intensive and time consuming distancing steps. The present invention is directed to fulfilling this need.